The detection and tracking of a target object or objects is typically accomplished with radio detection and ranging, commonly known as radar. Radar systems typically emit electromagnetic energy and detect the reflection of that energy scattered by a target object. By analyzing the time difference of arrival, Doppler shift, and various other changes in the reflected energy, the location and movement of the target object can be calculated. Phased array antenna systems employ a plurality of individual antenna elements or subarrays of antenna elements that are separately excited to cumulatively produce a transmitted electromagnetic wave that is highly directional. The radiated energy from each of the individual antenna elements or subarrays is of a different phase, respectively, so that an equiphase beam front or cumulative wave front of electromagnetic energy radiating from all of the antenna elements in the array travels in a selected direction. The differences in phase or timing among the antenna activating signals determines the direction in which the cumulative beam from all of the individual antenna elements is transmitted. Analysis of the phases of return beams of electromagnetic energy detected by the individual antennas in the array similarly allows determination of the direction from which a return beam arrives. Such processing as described above is well known to those of ordinary skill in the art.
A pulse based radar system scans a field of view and emits timed pulses of energy. Such radar systems, including, for example, CTA type radar systems, can require both short range and long range target detection and tracking. Long range (e.g. on the order of 60 kilometers (Km) or more) detection performance requires relatively long pulse repetition intervals (PRI). A narrow beam is typically required for long range target detection and tracking.
A conventional radar array having a plurality of radiating elements 100 configured to define an array aperture A for generating a narrow beam for long range detection and track performance is depicted in FIG. 1. The longer PRI reduces the probability of detecting high vertical velocity, shorter range targets (e.g. targets within about 15 Km). In order to alleviate this problem, systems may utilize separate short range (SR) and long range (LR) pulses in an attempt to cover all target ranges. However, even with SR pulses, significant limitations exist in conventional radar systems processing and implementation.
For example, short range detection and localization performance of conventional radar systems is typically not limited by target signal-to-noise ratio (SNR), but rather by the number of look opportunities of the target by the radar. This number is limited by such factors as high target vertical velocities, elevation beamwidth, and target revisit rate. More specifically, short range target detection and localization is usually not a function of SNR, because such short range targets typically have SNRs well in excess of typical threshold detection levels. However, the problem lies with the number of look opportunities with which to detect, track and localize a target with sufficient accuracy to evaluate a projectile launch or impact point. A radar system utilizing a narrow beam long range pulse for detecting and tracking targets may operate quite effectively for long range objects; however, such a system may be inadequate to track short range objects having high target vertical velocities, which require much greater processing and response time, but which does not require such narrow beam(s). Alternative techniques for detecting and tracking both long range and short range targets within a single radar system is desired.